This invention relates to an apparatus for detecting a crank angle and a cam angle in the control unit of an internal-combustion engine and also detecting the rotational speed of a driving system portion.
It has been well known to use a sensor having Hall elements in the form of an integrated circuit for detecting positions of a crank angle and a cam angle of an internal-combustion engine and also detecting a rotational speed in a driving system. The magnetic circuit of one known sensor includes an IC, and a magnet and a yoke core which are disposed on the back of the IC. Another known sensor includes a Hall IC and a magnet facing the Hall IC, so that the position of an object and the like are detected when the object passes therebetween.
Among those conventional sensors, a type called a differential type for detecting a magnetic material from a difference in output between two Hall elements within an IC has a magnetic circuit preformed for causing the magnetic flux to be substantially uniformly converged on the two elements. Then a comparator therein has been used to convert into pulses the differential value between both the elements and a differential value resulting from causing one of the elements to undergo response delay by means of a capacitor. Moreover, a magnet having a greater magnetic flux quantity has been employed for supplying a stable output.
As set forth above, an arrangement of two Hall elements in a differential Hall IC permits the magnetic flux to be substantially uniformly converged, so that an element-to-element output difference (hereinafter called the `magnetic flux change`) in the absence of a protrusion becomes equal to zero. Consequently, when the width of the protrusion is greater with respect to the direction of rotation, the magnetic flux change during the passage of the protrusion also becomes equal to zero as in the case where no protrusion exists. Therefore, the amount of delay in response because of the capacitor is minimized when the protrusion passing speed is low at the time of low-speed rotation, which results in greatly varying a position to be converted into a pulse. The basic magnetic flux change is extremely redundant and this has made the conversion to pulse difficult at a stable position.